The present invention relates to a resin-molding method, molding dies and a circuit base member and more particularly to a transfer molding technique, wherein plural semiconductor devices are bonded onto one face of a single circuit board for subsequent batch resin encapsulation of the plural semiconductor devices in a single cavity formed by molding dies.
The transfer mold has most-widely been used for the resin-encapsulation technique of semiconductor devices, wherein the plural semiconductor devices are bonded on a circuit base member, which includes a circuit board, a circuit film and a circuit tape for subsequently placing the semiconductor devices in a cavity of the dies, so that a molten resin is injected into a cavity by a plunger of a molding machine to carry out a resin-encapsulation of the semiconductor devices.
Plural semiconductor devices are aligned in matrix over a single Circuit base member for subsequent resin-encapsulation thereof. It is possible in one method to encapsulate the single package semiconductor devices with resin sequentially. It is also possible in another method to encapsulate the plural packages semiconductor devices with resin at one time. The later method, for example, the batch resin encapsulation is superior in high productivity and lower cost.
The single semiconductor package resin-encapsulation method is a method in which the semiconductor devices for one package are resin-encapsulated in one cavity different from other cavity in which other semiconductor devices for other package are independently resin-encapsulated. Side faces of the encapsulating resin are defined by the inner shapes of the molding dies. Independent plural encapsulating resins for individual packages are formed by the resin-molding process in the molding dies. It is unnecessary to carry out a dicing process for cutting or dividing the encapsulating resin. If any interconnection layer or any solder-resist layer is present on the circuit base member or on its cutting line such as a scribe line, it is necessary to cut the interconnection layer or the solder-resist layer.
The batch resin-encapsulation method is a method in which the semiconductor devices for plural packages are resin-encapsulated in a single cavity at one time. In accordance with this batch resin-encapsulation method, the encapsulating resin encapsulating the semiconductor devices for the plural packages is formed in a single flat panel-shape unit, which is so called as a package panel. It is, therefore, necessary to divide the package panel into plural semiconductor packages by dicing process. Side faces of the individual semiconductor package are defined by cutting in the dicing process. The batch resin-encapsulation method for the transfer molding may be carried out either using a release film or without using any release film. FIGS. 1A through 1D are fragmentary cross sectional elevation views illustrative of top and bottom dies and plural semiconductor devices bonded on a circuit base member using the sequential steps involved in the conventional batch resin-encapsulation method for the transfer molding with a release film. Molding dies 120 comprise a top die 121 and a bottom die 122. The top die 121 further comprises a top center block 24. The bottom die 122 further comprises a bottom center block 25 and a circuit base member mounting block 142. The bottom center block 25 is provided with a pot 27 which is to be filled with a resin 26. In the pot 27, the resin 26 is filled and further a plunger 28 is inserted for applying a pressure to the resin 26. The top center block 24 is provided with a caliber 29 at a position corresponding to the pot 27. Runners 30 as passages to a top cavity 23 for the molten resin 26 are formed in both sides of the caliber 29. The top die 121 has the top cavity 23a which accommodates plural semiconductor devices 12 bonded on the circuit base member 111, wherein the molten resin 26 is injected into the cavity 26 for encapsulating the semiconductor devices with the resin 26. The runners 30 formed in both sides of the caliber 29 are connected with a first side of the cavity 23a adjacent to the top center block 24. An air vent 146 is formed in a second side of the cavity 23a opposite to the first side. The air vent 146 relieves an inner gas in the cavity 23a upon injection of the molten resin into the cavity 23a. The air vent 146 comprises a channel groove formed in a cramp face of the top die 121. The bottom die 122 has a bottom cavity 23b at a corresponding position to the top cavity 23a of the top die 121. The bottom cavity 23b accommodates the circuit base member 111. The top and bottom cavities 23a and 23b form a closed or sealed cavity for sealing the circuit base member 111 and the semiconductor devices 12. The circuit base member 111 is mounted on the circuit base member mounting block 142. The circuit base member mounting block 142 is depressed from a circumferential block to form the bottom cavity 23b for accommodating the circuit base member 111. The circuit base member mounting block 142 is supported to be movable in up and down directions by a floating mechanism utilizing a spring member 43. The movements in up and down directions of the circuit base member mounting block 142 cause variation in depth of the bottom cavity 23b. The floating mechanism is needed for a board type circuit base member which is variable in thickness. If the floating mechanism is not used, then the bottom cavity 23b is kept in depth. Notwithstanding, if the thickness-variable circuit board is mounted on the circuit base member mounting block 142, this means that the surface level of the thickness-variable circuit board is thus variable. If the thickness of the circuit board mounted on the bottom cavity 23b is too thick relative to the fixed depth of the bottom cavity 23b, then an excess cramping pressure is applied to the board, whereby the board receives a damage. If the thickness of the circuit board mounted on the bottom cavity 23b is too thin relative to the fixed depth of the bottom cavity 23b, then an insufficient cramping pressure is applied to the board and a gap is formed, whereby a leakage of the molten resin from the gap appears. The floating mechanism is provided to solve the above problems caused by the variation in thickness of the circuit board. If the tape type circuit base member 111 is used, then the floating mechanism is not needed because the tape type circuit base member 111 is thin and variation in thickness of the tape type circuit base member ill is so small and causes no problem.
The top die 121 has an adsorption hole 44 for vacuum-adsorbing a release film. The adsorption hole 44 has an opening 44a adjacent to the top cavity 23a. The adsorption hole 44 provides a connection between the top cavity 23a and a non-illustrated external vacuum source. If no release film is needed or the dies, then it is unnecessary to provide the adsorption hole 44.
The resin molding machine not illustrated is provided with the dies 120. The resin molding machine further has a top base not illustrated for supporting the top die 121 and a bottom base not illustrated for supporting the bottom die 122 as well as has a heater not illustrated for heating the dies 120, a vacuum pump not illustrated and serving as a vacuum source and a cramping mechanism not illustrated and further an injection mechanism not illustrated. The resin molding machine further more has a plunger 28. The top and bottom dies 121 and 122 are fixed to the top and bottom bases by plates or volts respectively. The top base or the bottom base is elevated for closing motions of the dies 120.
The conventional batch resin molding method for molding the semiconductor devices and the method of forming the semiconductor devices will be described.
[Bonding Process]
A bonding process occurs prior to the resin-molding process. In the bonding process, semiconductor devices 12 for plural packages are arranged in matrix over a main face of a single circuit base member 111 and then bonded to the single circuit base member 111. The semiconductor devices 12 are wire-bonded to the single circuit base member 111. In FIGS. 1A, 1B and 1C, each of the semiconductor devices 12 is wire-bonded to the single circuit base member 111 by bonding wires 16. It is, however, possible that the semiconductor devices 12 are wireless-bonded to the single circuit base member 111, for example, by use of bumps. In any event, the semiconductor devices 12 are bonded to the single circuit base member 111.
[Pre-Cramping Process]
A pre-cramping process will be described with reference to FIG. 1A. The pre-cramping process is made following to the above bonding process. The circuit base member Ill is mounted on the circuit base member mounting block 142 of the bottom die 122. A release film 41 is placed so as to cover the top cavity 23a, the caliber 29 and the runners 30, wherein the release film 41 is vacuum-adsorbed onto the surface of the top cavity 23a, so that the release film 41 extends along the inner face shape. As a result, the opening 44a of the adsorption hole 44 is sealed with the release film 41. However, the release film 41 is capable of permeation of gas. The gas is transmitted through the release film 41 at a low flow rate and suctioned into the adsorption hole 44. Namely, the gas flow into the adsorption hole 44 is not completely stopped. The release film 41 makes it easy to release the molded resin 26 from the inner wall of the dies. If the release film 41 is not used, it is alternatively necessary to provide a pin in the holding part, so that the injection mechanism causes the pin to push the molded resin to release the molded resin from the inner wall of the dies, wherein a mold releasing agent may be periodically supplied to the inner wall of the top die 121, into which the molten resin 26 is injected for promoting the mold-release.
The circuit base member 111 and the release film 41 are heated by contacting with the dies 120 which have already been heated by the non-illustrated heater. Since the circuit base member 111 is heated from its back side, immediately after the circuit base member 111 is mounted on the circuit base member mounting block, a relatively large thermal expansion appears on the back side of the circuit base member 111, whereby the circuit base member 111 is bent or arched. This bending of the circuit base member 111 is, however, reduced upon a subsequent thermal equilibrium phenomenon. It is necessary to wait for the injection of the resin until disappearance of the bending of the circuit base member 111. Subsequently, a tablet type resin 26 is placed into the pot 27 of the bottom die 122.
[Cramping Process]
Subsequent to the pre-cramping process, the cramping process is made. The cramping process will be described with reference to FIG. 1B. The resin molding machine is operated to close the top and bottom dies 121 and 122 together for cramping the circuit base member 111 with the dies 120, wherein a circumferential portion of the circuit base member 111 is cramped by the top and bottom dies 121 and 122. The semiconductor device mounted region of the circuit base member 111 are not cramped directly and are confirmed in the cavity 23a. 
[Resin Injection Process]
The resin 26 is melted and the molten resin 26 is then injected by the plunger 28, so that the molten resin 26 is supplied through the caliber 29 and the runners 30 to the cavity 23a, whereby the cavity 23a of the dies 120 is filled with the injected resin 6. At the same time, the inner gas in the cavity 23a is pushed out of the cavity 23a through the air vent 146.
[Resin-Thermosetting Process]
After the dies 120 are filled with the resin 26, then the resin 26 is subjected to thermosetting, wherein the resin 26 comprises a thermosetting resin composition, whereby a package panel is completed. The dies 120 are opened for allowing the package panel with the release film 41 to be released from the dies 120 and further the used release film 41 is also removed from the package panel 41.
[External Terminal Formation]
If necessary, the external terminals are formed. In case of the ball grid array packages, solder balls as the external terminals are provided on the back side of the circuit base member 111.
[Package Dicing Process]
Subsequently, a package dicing process is made by use of a dicing machine with a circular blade which rotates for an abrasive grain cutting to the package panel, whereby the package panel is divided into plural semiconductor packages, wherein the side faces of each of the semiconductor packages are defined by the cutting faces by the circular blade.
The above conventional technique has the following problems. As shown in FIG. 1B, the cramping process with the dies 120 is made, whereby the circuit base member 111 is confirmed in the dies 120. At this time, a low pressure of the adsorption hole 44 is effected through the release film 41 to the circuit base member 111, so that the circuit base member 111 is suctioned toward the top die 121, whereby a center region of the circuit base member 111 is floated and the highest portion of the looped bonding wires 16 may be made into contact with the release film 41. This case will be referred to as a mode 1. As shown in FIG. 1C, the molten resin 26 is injected into the cavity 23a under high pressure, whereby one side of the circuit base member at the most deep portion of the cavity 23a is wrinkled and floated toward the top die 121. As a result, the highest portion of the looped bonding wires 16 may be made into contact with the release film 41. This case will be referred to as a mode 2.
In accordance with the investigations of the present inventors, it was confirmed that in case of the board type circuit base member 111, the above mode 1 is likely to appear, while in case of the tape type circuit base member 111, the above mode 2 is likely to appear.
The contact of the bonding wires 16 to the release film 41 provides a mechanical stress to the bonding wires 16 and causes undesirable deformation of the bonding wires 16. If a contact mark remains on the release film 41 and the resin molding is carried out, then the contact mark is transferred to the surface of the package panel, causing an appearance-defect of the semiconductor package. Such a semiconductor package is defective product and removed from the production line. Also, a semiconductor package with the contact mark may incorrectly be recognized so that the bonding wires are exposed or projected and the resin molding is improper, and then the semiconductor package is removed from the production line. Even if the semiconductor package is functionally okay, it is still difficult to deliver the semiconductor package to the client.
Japanese laid-open patent publication No. 8-142106 discloses that in order to prevent the floating of the circuit board, a vacuum adsorption is made to the circuit base member. It was confirmed by the present inventors that if the lower pressure effected by the release film adsorption means to the front surface of the circuit base member exceeds the low pressure effected by the circuit base member adsorption means to the back face of the circuit base member, then the circuit base member is floated in the mode 1.
If the circuit base member 111 is of the board type or the substrate type, the circuit base member mounting block 142 shows a floating motion, for which reason it is necessary to provide gaps between the circuit base member mounting block 142 and other blocks adjacent to the circuit base member mounting block 142. The gaps. However, cause leakage of vacuum, whereby the adsorption force effected to the back face of the board or substrate 111 is reduced. As a result, the circuit base member 111 is floated in the mode 1.
In the above Japanese laid-open patent publication No. 8-142106, it is also disclosed that the resin-molding machine is capable of resin-molding the plural semiconductor devices bonded to the plural substrates, wherein a peripheral region of the substrate around the semiconductor device is hold and cramped, so that it a substantive difference in pressure between the front and back sides of the substrate appears, the up and down movement of the substrate is not so large as the bonding wires or the semiconductor device are made into contact with the release film, whereby the above problems are not caused. The Japanese publication addresses that the vacuum adsorption to the substrate or board is made in order to suction the substrate or board and place the same on the top die before the cramping operation. The Japanese publication is silent on what the substrate or board is held after the cramping operation. The Japanese publication does not disclose nor teach the batch resin encapsulating technique for resin-molding the semiconductor devices for plural packages bonded on the single circuit base member. Accordingly, the Japanese publication provides no solution to solve the above problems engaged with the batch resin encapsulating technique.
If the above conventional technique disclosed in the above Japanese publication is applied to the resin-molding for the semiconductor devices for plural packages, the single circuit base member is first divided into the plural substrates before the resin-molding process is carried out to the individual resin-molding, wherein the peripheral region of the individual substrate is cramped. Accordingly, the conventional technique is independent from the above described serious problems engaged with the batch resin encapsulating technique.
In the above circumstances, it had been required to develop a novel resin-molding method and resin-molding dies as well as circuit base member free from the above problems.
Accordingly, it is an object of the present invention to provide a novel resin-molding method free from the above problems.
It is a further object of the present invention to provide a novel resin-molding method in the transfer mold technique to carry out the batch resin molding to the semiconductor devices for plural packages bonded on the single circuit base member in the single cavity of the molding dies, wherein the circuit base member is prevented from floating from the inner wall of the resin-molding dies to realize a high yield of the non-defective semiconductor packages.
It is a still further object of the present invention to provide novel resin-molding dies used for the resin-molding method in the transfer mold technique to carry out the batch resin molding to the semiconductor devices for plural packages bonded on the single circuit base member in the single cavity of the molding dies, wherein the circuit base member is prevented from floating from the inner wall of the resin-molding dies to realize a high yield of the non-defective semiconductor packages.
It is yet a further object of the present invention to provide a novel circuit base member used for the resin-molding method in the transfer mold technique to carry out the batch resin molding to the semiconductor devices for plural packages bonded on the single circuit base member in the single cavity of the molding dies, wherein the circuit base member is prevented from floating from the inner wall of the resin-molding dies to realize a high yield of the non-defective semiconductor packages.
The present invention provides a resin-molding method comprising the steps of: placing a circuit base member onto a mounting face of first one of paired dies, wherein a back face of the circuit base member is in contact with the mounting face placing the paired dies in a closing state for clamping a peripheral region of the circuit base member with the paired dies; and injecting a molten resin into a cavity of the paired dies for filling the cavity with the injected resin, wherein, in the closing state, a first pressure effected to a front face of the circuit base member is set higher in pressure level than a second pressure effected to the back face of the circuit base member, so as to secure the circuit base member to the mounting face.
The above and other objects, features and advantages of the present invention will be apparent from the following descriptions.